Automatic telephone system



Dec. 21, 1937. A. HEYDUCK UTOMATC TELEPHONE SYSTEM Filed Nov. 23, 1935 N`larin- Pw e.

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Patented Dec. 21, 1937 AUTOMATIC TELEPHONE SYSTEM;v

Alfred Heyduck, Berlin-Neuenhagen, Germany, assigner to Mix & GenestAktiengesellschaft, Berlin-Schoneberg, Germany, a company Y ApplicationNovember 23, 1935, serial No. 51,251 In Germany November 27, `1934 16Claims.

The invention refers to automatic telephone systemsr and moreparticularly to those arrangements for selectors thereof, by which thestation of a favored subscriber, for instance, can be switched to busylines, and it has for its object to speed up the operation of sucharrangements. This is accomplished in the following 'mannerz theselector, after having been engaged, will automatically step on, inresponse to each energizami; tion given by the station, to the next busyline and' will stop there. VConsequently it is not first necessary forthe subscriber to. listen whether a line with which he happens to beconnected, is free or busy, but he has the assurance fromv the la;beginning that he will be connected only with busy lines; that is tosay, he will be connected only with those lines over which conversationsare then taking place. i

'Ihe energization can be given through loop @y interruptions or bypressing a key. Interruption of the loop has the advantage that thesub-z scriber is in a position to skip a certain number of lines at onceby Vselecting a number corre-A spondingly higher than 1, a 0 forinstance. Through test switching means the circuit of the selectormagnet, established by the impulse receiving device, is automaticallymaintained until the next busy line has been reached. In order toprevent the selector from stepping on automatically as soon as a line onwhich the subscriber is just listening in becomes free, the test circuitis closed only temporarily.

The selector also steps on automatically over dead contacts, which canbe accomplished, for instance, by connecting the dead contacts; in thetest bank to the same potential (battery) as the free lines. If thestation has stepped theselector over all the lines, it will receive awarning signal indicating that all the lines have been 49 passed.Appropriately, the signal is connected to the rest position of theselector, so that it will serve at onceas a selector signal and, afterpassing overv all the contacts, as a warning signal. This has theadvantage that the listening selector can be used at the saine time as atraiiic meter device. That means that all the subscriber has to do is tocount how many times he has to press the key or how many times he has todial digit 1, respectively, in order to hear the acoustic signal again.The number of pressings of the key or the number of dialings,respectively, exceeds then by 1 the number of lines which are busy atthat moment.

It may now be desirable that it should also be possible for thesubscriber to switch over to a specific line, regardless of whether itis busy orfree. This happens, for instance, if the listen- -ing selectoris connected directly to P. B. X.

subscribers lines and if the favored station wants' 5. to watch thetraffic or the calls of a particular subscriber. For this purpose it ispossible to provide switching means which, depending on switchingmeasures of the favored station, permit of changing thelisteningfoperation of the selector in such a manner that the movementof this selector will be brought exclusively under the favored controlof the station, an automatic stepping up of the selector thus beingprevented. The invention is by Way of example explained hereafter withreference to the accompanying single figure of the drawing, which is aschematic circuit of an incorporation involving private branch exchangeswith selector operation. In this embodiment calls within the P. B. X.exchange are set up over local interconnecting trunks or links, whereaskoutside calls to the main exchange are connected to the outside trunklines by separate outside trunk selectors which are associated with theoutside trunks and which find the calling P., B. X. lines. Thearrangement according to this incorporation operates in such a mannerthat, if a favored station calls a special number so as to drive theimpulse receiver (i. e. the stepping switch of the local trunk) to acertain contact or to a certainv group of contacts, certain switchingdevices will be prepared which will upon the release of the local trunkconnect the favored P. B. X. station with the listening selector. Theoutside trunk lines are connected to the listening selector.

vThe private branch exchange shown in the drawing consists of local.trunks such as AS-LW and an outside trunk line selector AW, associatedwith outside trunk lines such as AL. Only one local trunk vand oneoutside trunk line with its outside trunk selector have been shown. Thedrawing also shows a listening selector AH (operated by a magnet MhW),over whose speech switching arms the favored P. B. X. station, rep- 45resented in the drawing, can step up to the outside trunk lines. Theconnection in this case goes over a monitoring coil MPL-Ue, which is ofsuch dimensions that the existing outside call will be only slightlydamped through the listening in. For this purpose the primary windinghas a larger number of turns than the secondary winding; condensers C2and C3 may amount, for

instance, to 0.5 mf.

A description will rst be given of local P. B. X. 55

connections and outgoing trunk line connections. Since known switchingoperations are here lnvolved, the details of the respective circuitarrangements are not shown.

The relays are denoted by capital letters, their contacts by therespective small letters.

A local P. B. X. connection is started simply by removing the receiverat the P. B. X. station N. Line relay R is energized over the followincircuit: i

-|-, RI, mhIV, tII, N; thence partly through tI, mhII, resistance (T)and partly through TI, TI,

Relay T can not operate in this circuit because it lies in shunt to theresistance (T). By the operation of relay R however common relay Anh isenergized, this being the starting relay for the local trunks: ground,TV, tIII, Anh,

At rI the winding ,TI of relay T is definitely separated and at rII thetest circuit for AS is prepared. By the pulling up of relay Ahh linefinder AS of a free local trunk is started by well known means which arenot shown in the drawing'. If the calling line is found, the followingtest circuit is established: ground, PHII, PHI, c-arm of AS, TII, thencethrough RII and TII in parallel,

Relay PH locks at phI over its low resistance winding I and therebyprovides a busy indication by lowering the test wire potential toprevent the intrusion of other connections in known manner. At phII andphIII the speech path to the supply bridge A, X of the line finder isswitched through. By the pulling up of T the calling potential of thesubscriber line is removed at tI and tII.

The P. B. X. subscriber now receives dial tone and with the aid of hisdial is in a position to set the line selector LW to the desired P. B.X. station by well known means not illustrated. When the call has beenthus set up relay P serves as test relay and relay Y as supply relay forthe called party.

If the P. B. X. station wishes to establish an outside trunk lineconnection, the P. B. X. subscriber will press the ground key n afterlifting the receiver. Winding RI is thereby short-circuited, wl'iile onthe other hand relay T can operate due to the amplification of currentin its winding I. At contact tI the shunt eld for winding TI iseliminated and at contact tII relay R is switched off and thesubscribers line wire is switched instead over rest contact rIII tocommon relay Amr., which serves as starting relay for outside trunkconnections. The test circuit for the outside trunk selector is preparedat tv.

By the pulling up of relay Ana the outside rimk selector AW of a freeoutside trunk line AL is energized by means not specifically shown so asto hunt for the calling subscriber. If this connection is found, a testrelay (not shown) pulls up over the cZ-path of the outside trunkselector in series with RII and TII. Relay R is also operated by theconnection whereby the call potentials are removed from the line, namelyat rI and TIII. At TII the test circuit over the dpath is broken, butthe low test-wire potential is maintained in known manner over thec-path arm of AW and consequently relays R and T remain energized. TheP. B. X. station N is now in connection with the outside trunk line andis in a position to call the desired outside exchange subscriber, as forexample by dialing if the out-v side exchange is of the automatic type.

If line finder AS of a local trunk has already been set to the callingline before the grounding key is pressed, differential relay X of theline finder is caused to operate through the pressing of the key n andby opening the holding circuit oi the local trunk at contact :c itcauses this trunk to be again released. Otherwise the switchingoperations are the same as `described in the preceding paragraph. v

If a subscriber at the favoured P. B. X. station Y N wishes to listen inon the outside trunk lines,

he begins rst 4of all by lifting the receiver, whereby he causes a freeline nder AS to be Set to his line, and he then dials the number 00.Winding VhI of a relay Vh is connected to the battery and is led tocontact il@ of the c-path of line selector LW. As soon as the lineselector is set to this contact, test relay P of the line selectoroperates and in series operates relay Vh. Furthermore, a. contact aI ofimpulse relay A oi the local trunk is connected to contact il@ of thert-path of line selector LW. Consequently, supply relay Y of the lineselector is energized at once over its winding I and the call current isthereby switched off by the usual means (not shown) which ordinarilytakes effect when a called subscriber answers. After relay Y has pulledup, the following circuit is established: ground, YII, b-arm of LW,d-arm of AS, y, darm of LW, MhII, mhiV, MhlII,

Slow acting relay Mhl starts to operate in this circuit. As can be seenfrom the drawing, the cir- Cuit flows over switching arm d of the linefinder. This gives the assurance that relay Mh! can be reached only bycertain stations, that is to say by favored P. B. X. stations. The:i3-contacts of AS are not wired at the other P. B. X. stations.

Relay Mh! locks over the c-arm and its con,- tact mhlII, and at onceopens its energizing circuit at mhlV. Relay Mh is energized at mhiI. AtmhlIII the c-contact of the line finder is grounded and relay P of linefinder AS is thereby caused to release through short-circuiting, so thatthe local trunk is released. Consequently, through interrupting thec-path of LW the holding circuit of relay Mhl is opened. After a delayinterval relay Mhl therefore releases. However, relay Mh is maintainedin the following manner: on releasing the local trunk relays R and T arereleased, so that contacts tI and tII return to their rest position.'Ihe following circuit is thereby established: MAI, DI, mhII, tI, N,tII, mhIV, DII, MAII,

Relay MA operates and switches nits contacts. Relay Mh, which is slowacting, is consequently maintained energized in the following circuit:ground, b'pII, malI, mhI, Mh, resistance,

With a contact mhI it is possible to prevent the favored P. B. X.station from being engaged by a line selector LW over the monitoringcoil MhUe during the listening in. If however that is to be permitted,contact mhIis short-circuited.

At contact mhV the energization of relay Vh. whose winding VhI wasdeenergized in releasing the local trunk, is prepared anew over windingVhII of this relay. As long as contact maIII is switched over, windingVhII is short-circuited, however. At mhIII the circuit for a hot wirerelay Hz' is interrupted, whose function is explained further on. AtmhVII and mhVIII the switching through of the speech path is preparedand at mhVI the circuit for the rotary magnet MhW of the listeningselector is prepared. The switching arms of this selector remain for thepresent in rest position (i. The favoured subscriber receives theselector signal over line WZ,

whose source of current was started at maII over' the line an. Thesubscriber at the Vfavored P. B. X. station now dials digit l inorder toset the listening selector to thefirst busy outside trunk line. Theswitching operations are as follows: At the first release of relay Macontact maIII returns to its rest position, whereby-the short circuitfor winding VhII is removed, so that this relay will be energized duringthe series of impulses. By opening contacts vhI and 'DhIII anyvdisturbance of the outside trunk lines that are to be rpassed isavoided. At maI-the rotary magnet MILW of the listening selector willreceive current in the followi ing circuit: groundmhini, mar', mhvr,Mew,

-. At the endofr the impulse, that is to say after relay MA hasagain'been operated, magnet MhW deenergizes again and consequently thelistening selector makes one step, so that' its switching arms reachposition I. If the outside trunk line connected with this step of thelistening selector is busy, then contact UI of this outside trunk lineis open, so thatl busy test relay BP will receive no current.Consequently, the selector remains in position I and, dueto thecontinuous short circuit at mhIII, relay Vh is ycaused to release. Atchi and at vhIII the switching through of Vthe speech path is effected,sothat therfavored subscriber can now listen in on the'first outsidetrunk line.

However, if the first outside trunk line is free, then contact vil ofthe rst outside trunk line has been closed and the following circuitA isestablished: y

dI, cI .of the rst outside trunk line, c-arrn' of MhW, BP; '12h11,shaft-controlled rest contact'wO (which closes `after leaving the restposition),

Relay BP operates in this circuit and again energizes magnet MhW atcontact bpI. At the same time the short-circuiting of relay Vh isfurther prevented, so that Vh will not release for the present. Thecircuit of test relay BP will now loe opened again at self-interruptorcontact of the selector magnet. Due to this, magnet MhW is againdeenergized at bpI, so that the selector will step up its switching arms`one step and consequently'steps on to position 2. If the second line isfree, too,`as has been assumed in the drawv i trunk line is connected.Relay BP cannot now operate again. Consequently, the selector stops atposition 3, relay WLY releases and at its contacts ohI and 'UhIII itswitches the monitoring coil Mlzle to outside trunk line 3.

The favored subscriber can now listen in on the conversation going onover this line. Ii the conversation is of no interest to him or if hewishes'to listen in on still another outsidel trunk line,fhe will againdial digit l and will thereby ,l step up the listening selector to thenext following busy outside trunk line, this being line 5. It should bementioned that contact 11h11 always closes only temporarily theenergizing circuit for the test relay. Consequently, if the selectorstands on a busy outside trunk line, that is to say if the subscriber islistening in, and if this line after a little while becomes free again,the listening selector will be prevented from turning automatically tothe next busy line to the annoyance of the subscriber. However, if onewishes to permit this automatic stepping up, then contact ULII wouldlhave to be short-circuited as shown by a dotted line in the drawing.

In the drawing it has been assumed that only rive outside trunk linesare connected to the selector, for instance because the private branchoutside trunk is only equipped for five outside trunk lines. Therefore,positions 6 and 1 of the listening selector are dead. It will now beassumed that the subscriber again ydials digit l, on the presumptionthat' there are vstillY other busy Voutside trunk lines.` In that case,thelistening selector will, to begin with, make one step in thedescribed manner, so that its switching arms reach position ii. To thedead positions 6 and 'l of arm c battery has been connected directly, sothat relay BP can operate in these two positions and that the selectorwill step automatically into rest position 1li. At this point thesubscriber again receives v the exchange signal, whose source of currenthas started anew over SO, maII, and the line an, and he knows therebythat the selector has passed overall the lines. If the subscriber hastaken notice of the number of dialing operations which were required toreceive the selector signal again, he will know the number of outsidetrunk lines busy at that particular moment.

In some instances it may be required that the favored subscriber beenabled to switch in on any desired line with the aid of the listeningselector, therefore also to free lines, especially if the listeningselector is connected directly to the P. B. X. subscriber lines insteadof to the outside trunk line. Consequently, the listening selector mustbe prevented from passingautomatically over the free lines. For thispurpose diierential relay D has been provided. If the 'favoredsubscriber presses the grounding key at his-station at any time afterengaging theY listening selector, differential relay D operates and iscaused to hold itself over maIV and dII and its winding DIII. At contactdI the battery potential is switched from contact ci and the operationvof relay BP is thereby prevented. Accordingly, magnet MhW of thelistening selector is now exclusively under the control of contact mal,that is to say under the exclusive control of the subscribers dial,.sothat he can control the listening selector and set it to any desiredline, for instance also by dialing a higher digit than 1.

The arrangement can also be such that the listening selector can bereached by means of different indicator digits, for instance 'by meansof indicator @Sin addition to mi. On dialing indicator 09, for instance,a discriminating relay will operate only in this case but will notope-rate if indicator il!) is dialed. This relay could take the place ofdifferential relay D, which is energized by Vpressing the grounding,key, and the functions of which it could take over.

If the subscriber at P.- B. X. station N replaces this receiver at anytime, relay MA is released, so

` that relay Mh is continuously short-circuited.

Mh therefore releases and at mhVl closes a selfinterrupting circuit formagnet MLW. The latter is stepped up with the aid of itsself-interrupting contact until it reaches the rest position,consequently where contact 'wO opens.

If indicator @il is dialed by an unauthorized P. B. X. station, relay Vhwill pull up over its winding I but relay MhI can not operate because,as already explained before its circuit is opened in contact bank of armd' of the line iinder. However, hot wire relay Hi is heated over mhIII,

vhIV. Therefore, if the subscriber does not replace the receiver atonce, the hot wire relay has time to switch its contact, thus causingrelays P and VhI to be short-circuted. Through the release of relay Pthe line selector is busied and the subscriber receives the busy signal.

What is claimed is:

l. In a telephone system a selector actuated by a magnet and adapted toconnect a station of the system to busy lines, means at the said stationfor producing loop interruptions, an impulse receiving device responsiveto said interruptions for causing the energization of the magnet of theselector and auxiliary means effective to continue the driving of saidselector as long as said selector is connected to a non-busy line.

2. In a telephone system, a selector operated by a magnet and adapted toconnect a station to busy lines, means for producing at the said stationa variable number of loop interruptions, an impulse receiving devicevariably responsive to said interruptions in dependence on their number,means for transmitting a correspondingly variable energization to themagnet of the selector, and test switching means for continuing theenergization of this magnet until the next following busy line isreached.

3. A telephone system, comprising a selector operated by a magnet andadapted to connect a station to busy lines, means for producing at thesaid station loop interruptions, an impulse receiving device adapted toenergize said magnet responsive to said interruptions, test switchingmeans for continuing the energization of this magnet until the nextfollowing busy line is reached, and means for rendering the said testswitching means only temporarily effective, so as to prevent theautomatic stepping up of the said selector if a busy line just beingtested becomes free.

4. A telephone system according to claim 1 further comprising means forstepping the said selector over dead bank contacts thereof in responseto an electrical condition of said contacts.

5. A telephone system according to claim 1 comprising means for giving awarning signal to the said station in response to the passage of thesaid selector over all the lines.

6. A telephone system according to claim 1 comprising means for giving awarning signal to the said station in response to the passage of saidselector over all the lines, this signal being associated with the homeposition of this selector and being adapted to serve also as a dialtone.

'7. A telephone system according to claim 1, comprising means forchanging the mode of operation of the said selector, such means beingunder the control of the said station.

8. In a private branch exchange system having local lines and outsidelines, a selector adapted to switch a local line of this system to busylines, means adapted to respond to control signals received over saidlocal line for causing said selector to hunt for and connect tothe nextbusy line, a local trunk having a digit impulse receiver, switchingmechanism adapted to release the said local trunk and to connect saidlocal line tol the said selector, and means for operating said switchingmechanism in response to a predetermined setting of said digit impulseIeCelVeI.

9. A system according to claim 8 further comprising means effective onlywith respect to one particular local line for giving the local lineaccess to said selector.

10. A system according to claim 8, in which said selector makesconnections to said outside lines.

11. In a system according to claim 8, a talking current supply relay insaid local trunk and means for energizing this relay over the speecharms of this local trunk in response to a predetermined setting of theimpulse receiver of said trunk.

12. A system according tol claim 8, wherein the said switching mechanismis included in the test circuit of the said selector.

13. A system accor-ding to claim 8, comprising a supply relay in saidlocal trunk, a primary line switch for connecting said local trunk tosaid local line, a special relay adapted to be operated by currentthrough this supply relay and over a switching arm of the said primaryswitch, said special relay being a member of the said switching deviceswhich are adapted to release the said local trunk and to connect thesaid local line to said selector.

14. A system according to claim 8, in which said switching devices,which are adapted to release the said local trunk and to connect thesaid local line to the said selector comprise a relay associated withsaid local line for controlling the connection of the said local linewith the said selector, said relay being adapted to hold itself afterthe release of said local trunk and also to protect said local lineagainst other engagement.

15. In a system according to claim 8, means for completing theconnection of said local line to said selector only if said local lineis a predetermined one of the local lines of the system, and a timingswitch for giving a signal to any one of the other local lines inresponse to an attempted connection of the latter to said selector.

16. In a system according to claim 8, meansfor giving the said localline access to said selector only if said local line is a predeterminedone of the local lines of the system, a test relay for the said localtrunk, a timing switch adapted to short-circuit this relay, means forenergizing this timing switch in response to the reception over anyother of the local lines of signals such as are used to connect thepredetermined local line to the selector and means, controlled by saidshort-circuit, for transmitting a signal over said other local line.

ALFRED HEYDUCK.

